1,058 research outputs found

    Robot Assisted Laser Osteotomy

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    In the scope of this thesis world\u27s first robot system was developed, which facilitates osteotomy using laser in arbitrary geometries with an overall accuracy below 0.5mm. Methods of computer and robot assisted surgery were reconsidered and composed to a workflow. Adequate calibration and registration methods are proposed. Further a methodology for transferring geometrically defined cutting trajectories into pulse sequences and optimized execution plans is developed

    Optical Coherence Tomography guided Laser-Cochleostomy

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    Despite the high precision of laser, it remains challenging to control the laser-bone ablation without injuring the underlying critical structures. Providing an axial resolution on micrometre scale, OCT is a promising candidate for imaging microstructures beneath the bone surface and monitoring the ablation process. In this work, a bridge connecting these two technologies is established. A closed-loop control of laser-bone ablation under the monitoring with OCT has been successfully realised

    Laser in Orthodontics

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    Ultrashort-pulsed laser ablation of poly-L-lactide (PLLA) for cell and tissue engineering applications

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    El contenido de los capítulos 3 y 4 están sujetos a confidencialidad 167 p.La tecnología de ablación láser es una herramienta bien establecida para la modificación superficial de materiales de distinta naturaleza (metales, polímeros, cerámicas, vidrio¿). La ablación de material mediante láseres de pulso ultracorto (menor que 10 picosegundos) es capaz de generar motivos topográficos micrométricos con una alta precisión debido a un proceso de ablación ¿frío¿ minimizando los efectos térmicos en el material sin producir cambios químicos en el mismo. Es por tanto una tecnología versátil para la fabricación de superficies microestructuradas en un proceso directo y sin contacto y aplicable a una gran variedad de materiales para generar motivos con distintas geometrías sobre superficies no planas. En este trabajo de tesis se aplica la tecnología de ablación mediante láser pulsado de picosegundos para la creación de micro-patrones topográficos en planchas de ácido poli-L-láctico (PLLA), para investigar el mecanismo de ablación del mismo y el efecto de los micro-patrones en el comportamiento de varios tipos de células mediante ensayos in vitro, con el objetivo final de elucidar el alcance de la influencia de estos micro-patrones en el comportamiento celular y evaluar la tecnología como método de fabricación de soportes en la ingeniería de tejidos

    A Magnetic Laser Scanner for Endoscopic Microsurgery

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    Laser scanners increase the quality of the laser microsurgery enabling fast tissue ablation with less thermal damage. Such technology is part of state-of-the-art freebeam surgical laser systems. However, laser scanning has not been incorporated to fiber-based lasers yet. This is a combination that has potential to greatly improve the quality of laser microsurgeries on difficult-to-reach surgical sites. Current fiberbased tissue ablations are performed in contact with the tissue, resulting in excessive thermal damage to healthy tissue in the vicinity of the ablated tissue. This is far from ideal for delicate microsurgeries, which require high-quality tissue incisions without any thermal damage or char formation. However, the possibility to perform scanning laser microsurgery in confined workspaces is restricted by the large size of currently available actuators, which are typically located outside the patient and require direct line-of-sight to the microsurgical area. Thus, it is desired to have the laser scanning feature in an endoscopic system to provide high incision quality in hard-to-reach surgical sites. This thesis aims to introduce a new endoscopic laser scanner to perform 2D position control and high-speed scanning of a fiber-based laser for operation in narrow workspaces. It also presents a technology concept aimed at assisting in incision depth control during soft-tissue microsurgery. The main objective of the work presented in this thesis is to bring the benefits of free-beam lasers to laser-based endoscopic surgery by designing an end-effector module to be placed at the distal tip of a flexible robot arm. To this end, the design and control of a magnetic laser scanner for endoscopic microsurgeries is presented. The system involves an optical fiber, electromagnetic coils, a permanent magnet and optical lenses in a compact system for laser beam deflection. The actuation mechanism is based on the interaction between the electromagnetic field and the permanent magnets. A cantilevered optical fiber is bended with the magnetic field induced by the electromagnetic coils by creating magnetic torque on the permanent magnet. The magnetic laser scanner provides 2D position control and high-speed scanning of the laser beam. The device includes laser focusing optics to allow non-contact incisions. A proof-of-concept device was manufactured and evaluated. It includes four electromagnetic coils and two plano-convex lenses, and has an external diameter of 13 mm. A 4 74 mm2 scanning range was achieved at a 30 mm distance from the scanner tip. Computer-controlled trajectory executions demonstrated repeatable results with 75 m precision for challenging trajectories. Frequency analysis demonstrated stable response up to 33 Hz for 3 dB limit. The system is able to ablate tissue substitutes with a 1940 nm wavelength surgical diode laser. Tablet-based control interface has been developed for intuitive teleoperation. The performance of the proof-of-concept device is analysed through control accuracy and usability studies. Teleoperation user trials consisting in trajectory-following tasks involved 12 subjects. Results demonstrated users could achieve an accuracy of 39 m with the magnetic laser scanner system. For minimally invasive surgeries, it is essential to perform accurate laser position control. Therefore, a model based feed-forward position control of magnetic laser scanner was developed for automated trajectory executions. First, the dynamical model of the system was identified using the electromagnets current (input) and the laser position (output). Then, the identified model was used to perform feedforward control. Validation experiments were performed with different trajectory types, frequencies and amplitudes. Results showed that desired trajectories can be executed in high-speed scanning mode with less than 90 m (1.4 mrad bending angle) accuracy for frequencies up to 15 Hz. State-of-the-art systems do not provide incision depth control, thus the quality of such control relies entirely on the experience and visual perception of the surgeons. In order to provide intuitive incision depth control in endoscopic microsurgeries, the concept of a technology was presented for the automated laser incisions given a desired depth based on a commercial laser scanner. The technology aims at automatically controlling laser incisions based on high-level commands from the surgeon, i.e. desired incision shape, length and depth. A feed-forward controller provides (i) commands to the robotic laser system and (ii) regulates the parameters of the laser source to achieve the desired results. The controller for the incision depth is extracted from experimental data. The required energy density and the number of passes are calculated to reach the targeted depth. Experimental results demonstrate that targeted depths can be achieved with \ub1100 m accuracy, which proves the feasibility of this approach. The proposed technology has the potential to facilitate the surgeon\u2019s control over laser incisions. The magnetic laser scanner enables high-speed laser positioning in narrow and difficult-to-reach workspaces, promising to bring the benefits of scanning laser microsurgery to flexible endoscopic procedures. In addition, the same technology can be potentially used for optical fiber based imaging, enabling for example the creation of new family of scanning endoscopic OCT or hyperspectral probes

    Surface functionalization with antibacterial and bioactive compounds using hybrid techniques (subtractive and addictive) via laser for the improvement of knee prostheses properties

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    Dissertação de mestrado integrado em Biomedical Engineering (área de especialização em Biomaterials, Rehabilitation and Biomechanics)Knee arthroplasty is a surgical procedure that consists in the removal of the entirety or part of the knee joint, extracting damaged cartilage and replacing it with a prosthesis or implant. Thus, knee prostheses are devices that replace the function of the joint. They have different components, each with a specific function and composed of different materials. However, their longevity is still relatively short, about 15 years, and the use of materials with inadequate mechanical properties can lead to the appearance of undesirable phenomena that contribute to an even earlier prosthesis removal. That being said, it is important to find solutions to improve not only the functionality of these implants, but also their longevity. Therefore, this work focuses on the modification of materials typically used in these implants, such as zirconia and titanium, through a hybrid (subtractive and additive) laser processing technique. Patterns were thus created on the surface of the materials, and bioactive compounds (hydroxyapatite and mineral trioxide aggregate) were incorporated into them, in order to improve the bioactivity and consequent functionality and longevity of the knee prostheses. Firstly, samples of the base materials in question were created and textured using different strategies and varying laser parameters such as power, speed and number of passes. The bioactive materials were then deposited and incorporated on the surface of the samples using different techniques, such as CO2 laser sintering, conventional furnace method or deposition using a spatula. Finally, mechanical tests were performed in order to analyse and evaluate the properties of the produced samples. These include SEM-EDS, wettability, friction tests and cell viability tests. Results show that the laser texturing was considered an effective and reliable method to produce different structures throughout the samples without compromising its mechanical properties. The employed functionalization techniques were successful, as mechanically interlocked and thick coatings were created. The incorporation of said coatings had a significant effect on the surface energy of the samples, since wettability tests showed that contact angle of the samples is reduced after the addition of the bioactive layer. Friction tests comproved the adherence of bone to the surface of functionalized samples, while biological tests revealed the bioactive potencial of the MTA coating. In conclusion, textured samples were successfully produced and afterwards functionalized using different techniques. These surfaces showed promising results in both mechanical and biological tests, as this new approach for the development of functionalized knee prostheses is validated.A artroplastia do joelho é um procedimento cirúrgico que consiste na remoção da totalidade ou de parte da articulação do joelho, retirando cartilagem danificada e substituindo a mesma por uma prótese ou implante. Assim, as próteses do joelho são dispositivos que substituem a função da articulação, possuindo diferentes componentes, cada um deles com uma função específica e compostos por materiais distintos. No entanto, a sua longevidade é ainda relativamente curta, de cerca de 15 anos, e a utilização de materiais com propriedades mecânicas desadequadas levam ao aparecimento de fenómenos indesejáveis que contribuem para a remoção da prótese de forma precoce. É então importante encontrar soluções para melhorar não só a funcionalidade destes implantes, mas também a sua longevidade. Assim, este trabalho foca-se na modificação de materiais tipicamente usados nestes implantes (zircónia e titânio) através de uma técnica de processamento híbrida (subtrativa e aditiva), via laser. Foram assim criados padrões na superfície dos materiais, e incorporados neles compostos bioativos (hidroxiapatite e agregado de trióxido mineral), de modo a melhorar a bioatividade e consequente funcionalidade e longevidade das próteses do joelho. Primeiramente, foram criadas e texturizadas as amostras dos materiais base em questão, utilizando diferentes estratégias e variando parâmetros do laser, como a potência, velocidade e número de passagens. Os materiais bioativos foram posteriormente incorporados na superfície das amostras através de diferentes técnicas, como sinterização a laser, forno ou deposição com recurso a uma espátula. Por último, foram efetuados testes mecânicos de modo a analisar e avaliar as propriedades das amostras produzidas, como o SEM-EDS, molhabilidade, testes de fricção e testes de viabilidade celular. Resultados mostram que a texturização a laser foi considerada um método eficiente na produção de diferentes estruturas superficiais. As técnicas de funcionalização foram bem-sucedidas, já que camadas espessas de bioativos foram aprisionadas na superfície. A adição destes materiais afetou a energia da superfície, já que os testes de molhabilidade mostraram uma redução do ângulo de contacto após deposição. Testes de fricção comprovam a adesão de osso na superfície das amostras funcionalizadas, enquanto que os testes biológicos revelaram o potencial bioativo do revestimento de MTA. Concluindo, amostras texturizadas foram produzidas e posteriormente funcionalizadas através de técnicas variadas. Estas superfícies demonstraram resultados promissores tanto em termos biológicos como mecânicos, sendo a abordagem de funcionalização proposta validada

    Study of zirconia antibacterial surfaces for application on dental Implants

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    Dissertação de Mestrado (Ciclo de Estudos Integrados Conducentes ao Grau de Mestre em Engenharia de Materiais)Dental implants are currently the most reliable solution for dental replacement. Although Titanium alloy (TiAl4V) is considered the gold standard dental implant material, some disadvantages have been pointed such as metallic ions release and its greyish colour that can be visible through fine mucosa. Zirconia (ZrO2) is a bioceramic that has been studied as a promising metal-free alternative to titanium due to its good biocompatibility, good mechanical properties compared to other ceramics, good aesthetic, due to its tooth-like colour and low affinity to bacterial microorganisms. Despite the high rate of successful dental implants, problems related to the entry and proliferation of bacteria to the peri-implant zone have been emerging. Peri-implantitis is the most frequent biological cause that leads to implant failure and immediate implant removal. Thus, is extremely important to develop a zirconia surface with antibacterial properties to apply in dental implants. In this context, the present dissertation addresses the study of a barrier approach to inhibit the penetration of microorganisms into the peri-implant zone through the production of successive microgrooves and a biocide approach to eliminate the bacteria that interact with the implant by silver and gold surface chemical functionalization. The microgrooves were produced by an Nd:YAG laser, morphologically characterized by SEM and tested for their retention capacity to artificial soft tissue by mechanical tensile test. Its roughness was also evaluated. The micro-functionalization with silver (Ag) was performed in a two-step process of cold pressing and laser sintering via Nd:YAG laser. And the gold (Au) nano-functionalization was tested by three different methods from which one was selected. Thus, the Au nano-functionalization was carried out by deposition by spray and sintering via CO2 laser. The chemical functionalized samples were subjected to reciprocating friction tests against bone to simulate implant insertion and then analysed through SEM/EDS. The results achieved showed that the introduction of microgrooves on zirconia surface increased the mechanical retention to artificial soft tissue. Roughness evaluation revealed the need for an improvement on laser finishing. The chemical functionalized surfaces presented good resistance to the friction test against bone. Additionally, the obtained COF values can predict good primary stability of the implant. The modified surfaces revealed promising results in the context of the application.Os implantes dentários são atualmente a solução mais confiável para a substituição dentária. Embora a liga de Titânio (TiAl4V) seja considerada o material de excelência em implantes dentários, algumas desvantagens têm sido apontadas, como a libertação de iões metálicos e a sua cor acinzentada que pode ser visível através da gengiva fina. A Zircónia (ZrO2) é uma biocerâmica que tem vindo a ser estudada como uma promissora alternativa ao Titânio, devido à sua boa biocompatibilidade, boas propriedades mecânicas comparativamente a outras cerâmicas, boa estética devido à sua cor clara e à baixa afinidade para com as bactérias. Apesar da elevada taxa de sucesso dos implantes dentários, têm surgido problemas relacionados com a entrada e proliferação de bactérias na zona peri-implantar. A periimplantite é a causa biológica mais frequente da falha do implante. Sendo assim, torna-se importante desenvolver uma superfície em Zircónia com propriedades antibacterianas. Neste contexto, a presente dissertação contempla o estudo de uma abordagem de barreira para inibir a penetração de microrganismos na zona peri-implantar através da produção de micro rasgos sucessivos á superfície e uma abordagem biocida para eliminar as bactérias que interagem com o implante por funcionalização química da superfície com prata e ouro. Os rasgos foram produzidos através de um laser Nd: YAG e foram avaliados quanto à sua retenção em gengiva artificial com testes de tração uniaxial. A sua rugosidade também foi avaliada. A micro-funcionalização foi realizada com prata (Ag) por um processo de prensagem a frio seguida de sinterização a laser Nd: YAG e a nano-funcionalização foi realizada com ouro (Au) e foi testada por três métodos dos quais um foi selecionado. Assim sendo, a nanofuncionalização com Au foi realizada por deposição por spray e sinterização via laser de CO2. As amostras resultantes foram submetidas a ensaios de atrito e analisadas através de microscopia eletrónica de varrimento e espectroscopia dispersiva de raios-X. Os resultados demostraram que a introdução de rasgos na superfície em Zircónia aumentou a retenção mecânica da gengiva artificiais. A avaliação da rugosidade revelou a necessidade de uma melhoria deste parâmetro. As superfícies obtidas através da funcionalização química apresentaram boa resistência ao teste de atrito. Além disso, os valores de COF obtidos preveem uma boa estabilidade primária do implante. As superfícies modificadas revelam resultados promissores no contexto da aplicação.This work was supported by FEDER funds through the COMPETE 2020 – Programa Operacional Competitividade e Internacionalização (POCI) with the reference project POCI-01-0145-FEDER-006941 and POCI-01-0145-FEDER-030498 and the project with reference NORTE-01-0145-FEDER-000018-HAMaBICo

    Theranostic Gelatin Nanoparticles for Antigen Delivery and Combined Strategies for Transcutaneous Application

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    Transcutaneous application of vaccines is a promising strategy to enhance the effectiveness of vaccination using a reachable route of administration. Additionally, replacing the conventional needles with skin mechanical penetration techniques as microneedles or skin laser microporation will offer great advantages. This transcutaneous delivery techniques are pain-free and will help to avoid the hazards of needles. For the delivery of antigens, nanocarriers are so promising to enhance and modulate their immune response. The nanocarriers offer merits such as antigen protection from degradation, and controlling the release rate of the antigen. Additionally, due to the particulate nature of the nanocarriers, they can potentially display the antigen in a way that better mimics pathogens. For this aim, ovalbumin as a model antigen has been delivered using functionalized theranostic gelatin nanoparticles to bone marrow-derived dendritic cells (BMDCs). The nanoparticles were rendered fluorescent by using a novel imaging agent (gold and silver alloy nanoclusters) that emits near-infra red light. This was beneficial to study the nanoparticles uptake by BMDCs and also to image the nanoparticles within the skin tissue. Finally, the developed theranostic nanocarriers induced the maturation of the BMDCs and enhanced the proliferation of both helper T cells (CD4+) and cytotoxic T cells (CD8+). This indicates the potential efficacy of the delivery system for vaccination either against allergy or viruses and tumors

    Comparing Gaussian and Bessel-Gauss beams for translating ultrafast laser ablation towards soft tissue surgery

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    The goal of this research was to further improve existing ultrafast laser surgery techniques. To do so, different beam shapes (Bessel-Gauss and Gaussian) were compared for performing ultrashort picosecond pulsed surgery on various soft biological tissues, with the goal of minimising collateral thermal damage. Initially, theoretical modelling was performed using OpticStudio to test axicons of various conical angles. A 20° axicon was selected, but unfortunately early tests on murine intestinal tissue indicated a lack of sufficient intensity to achieve plasma-mediated ablation of the tissue with the 6ps input pulses of 85 µJ energy. Subsequently, a reimaged setup was designed in OpticStudio to demagnify the beam by a factor of 1.4x. The ability of this demagnified Bessel-Gauss beam to perform plasma-mediated ablation of murine intestinal tissue was confirmed through histological analysis. Another setup was also designed to produce a Gaussian beam of equivalent spot size. These beams were then tested on porcine intestinal tissue using lower pulse repetition rates of 1, 2 and 3 kHz, with optimal ablation and thermal damage margins of less than 20 µm (confirmed through histological analysis) being achieved with the Bessel-Gauss beam for spatial pulse overlaps of 70%, while for the Gaussian beam the prominence of cavitation bubble formation at both 2 and 3 kHz inhibited the respective ablation processes at this same spatial pulse overlap. As the numbers of passes were increased, the Bessel-Gauss beam also showed a trend of increased ablation depths. This was attributed to its large depth of focus of over 1 mm, compared to the theoretical 48 µm depth of focus for the Gaussian beam. After characterisation of fixated, non-ablated porcine intestine sample surfaces to quantify the inhomogeneity, another set of ablation trials was performed at higher pulse repetition rates (5, 10 and 20 kHz) to test more clinically viable processes. For the Bessel-Gauss beam, spatial pulse overlaps of up to around 50% at 5, 10 and 20 kHz offered excellent thermal confinement (with damage margins of < 30 µm, < 50 µm and < 25 µm respectively) and shape control, but at 70% and greater pulse overlaps the ablated feature became hard to control despite good thermal confinement (< 40 µm). The Gaussian beam, while having the advantage of achieving plasma formation at lower input pulse energies, was again found to be more prone to undesirable cavitation effects. Cavitation bubbles were observed in the histology images for spatial pulse overlaps as low as 15% for 5 kHz and 30% for both 10 and 20 kHz. From the histology images it is clear to see that these effects became more pronounced as the pulse repetition rate was increased. Conversely, the more consistent spot size of the Bessel-Gauss beam across its longer focal depth resulted in a higher tolerance to cavitation bubble formation. This was also demonstrated by high-speed videos of the beams being scanned across porcine skin samples. This could be significant as it may allow for higher ablation rates. In addition, it could ease the design constraint of the maximum speed at which the beam can be scanned at the distal end of an endoscopic device. Despite this, both beams were able to achieve distinct ablation with high thermal confinement for certain parameters. This work further highlights fibre-delivered ultrashort laser pulses as a promising alternative to existing endoscopic tumour resection techniques, which carry a higher risk of bowel perforation.James Watt Scholarshi

    Current Research in Pulsed Laser Deposition

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    Despite its limitation in terms of surface covered area, the PLD technique still gathers interest among researchers by offering endless possibilities for tuning thin film composition and enhancing their properties of interest due to: (i) the easiness of a stoichiometric transfer even for very complex target materials, (ii) high adherence of the deposited structures to the substrate, (iii) controlled degree of phase, crystallinity, and thickness of deposited coatings, (iv) versatility of the experimental set-up which allows for simultaneous ablation of multiple targets resulting in combinatorial maps or consecutive ablation of multiple targets producing multi-layered structures, and (v) adjustment of the number of laser pulses, resulting in either a spread of nanoparticles, islands of materials or a complete covering of a surface. Moreover, a variation of PLD, known as Matrix Assisted Pulsed Laser Evaporation, allows for deposition of organic materials, ranging from polymers to proteins and even living cells, otherwise difficult to transfer unaltered in the form of thin films by other techniques. Furthermore, the use of laser light as transfer agent ensures purity of films and pulse-to-pulse deposition allows for an unprecedented control of film thickness at the nm level. This Special Issue is a collection of state-of-the art research papers and reviews in which the topics of interest are devoted to thin film synthesis by PLD and MAPLE, for numerous research and industry field applications, such as bio-active coatings for medical implants and hard, protective coatings for cutting and drilling tools withstanding high friction and elevated temperatures, sensors, solar cells, lithography, magnetic devices, energy-storage and conversion devices, controlled drug delivery and in situ microstructuring for boosting of surface properties
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